The present invention relates to power source circuitry built into a portable radio telephone and, more particularly, to power source control circuitry for a portable radio telephone for automotive use which is powered by an on-board power source, or battery, via an adapter.
A mobile radio telephone implemented as a portable telephone for use on a motor vehicle is mounted on an adapter which is connected to an on-board power source or battery. Power source control circuitry is connected between the battery and the adapter to control the supply of power from the battery to the telephone through the adapter which serves as an interface. Conventional power source control circuitry has a switch circuit for switching the connection of the battery and adapter on and off, a power ON/OFF sensing circuit responsive to a turn-on and turn-off power switch built into the telephone, and a switch control circuit for controlling the switch circuit. Implemented by a flip-flop, the power ON/OFF sensing circuit inverts, every time the power switch is turned on or off, the logical level of the resultant line pulse and holds the inverted output thereof. The switch control circuit ANDs the output of the power ON/OFF sensing circuit and the output of an ignition switch of the vehicle to turn on the switch circuit, thereby establishing the connection of the battery and adapter. Once the power ON/OFF sensing circuit inverts the logical level in response to an ON output of the power switch of the telephone, it holds the inverted output thereof since it is implemented by a flip-flop, as mentioned above. As a result, once the power switch of the telephone is turned on, the connection of the battery and adapter is switched on and off solely by the ON/OFF signal of the ignition switch. This brings about a problem that even when the telephone is removed from the adapter which is connected to the battery, power is wastefully fed from the battery to the adapter, causing unnecessary power consumption.